Vodacom robbing me as a loyal customer

My name is PE Malatji, I have two contracts with Vodacom, 0ne for 064 and the second one is a 076 number which I use for Data. Previously I was paying around R139.00 for 2 gig of data before I took another contract which I paid R359.00. Upon receiving the new contract in November 2016 for the 064 number, I then contacted Vodacom to request for a cancellation of the 2 gig data number as it had already expired. I was convinced by a customer care consultant not to cancel the contract but rather continue with it subject to a reduced fee of around R40.00 for 500 megabytes of data and a discount on my 064 number from R359.00 to R299.00. I agreed to the terms hence I did not cancel the data contract. The overall amount for the two contracts combined was R338.99. That agreement continued till the 15th of November 2017. On 15 December 2017, Vodacom decided to unilaterally change the contract premium to R395. 82. I called customer care several times and I was taken from pillar to post until I was told that I will be credited for the mistake. On 15 February 2018, instead of paying R395.82, I only paid around R33.00 because I was credited. I even received an sms to indicate that my query was resolved. To my surprise when I received my March bill, the amount went back to the R395.82 which I have queried previously. I complained again in March and I was credited again in April where I paid R261.01. Now in May, the amount has again gone back to R396.00. This is totally unacceptable because I have been calling their call centre and no one seems to care. This a top up contract and the premium cannot fluctuate from month to month. I am now considering cancelling both contracts because Vodacom has unilaterally deviated from the contract agreement. This company is robbing me daylight. They can go through my account and see what they are doing to me. Angry loyal customer